TacoRabbit

It's also worth noting that if you're concerned about Epic Changing the Deal and doing a rugpull like Unity, they've said you can simply not accept the changes and continue operating under your existing terms you agreed to:

"If we make changes to this Agreement, you are not required to accept the amended Agreement, and this Agreement will continue to govern your use of any Licensed Technology you already have access to."

You potentially lose access to epic services of various sorts, but it's a far cry from the Unity situation.

https://www.unrealengine.com/en-US/eula/unreal (Section 7)

Not only is it not just a theory, it's actually used in Medicine!

For example, PET Scans use positrons: https://en.wikipedia.org/wiki/Positron_emission_tomography